When a pressure-sensitive adhesive sheet is manually applied to an adherend, air entrapments may occur between the adherend and the pressure-sensitive adhesive face thereby to detract the appearance of the pressure-sensitive adhesive sheet. Such air entrapments readily occur, particularly when the surface area of the pressure-sensitive adhesive sheet is large.
In addition, resin materials such as acrylic resin, ABS resin, polystyrene resin and polycarbonate resin may generate gases due to heating or other treatments, and if a pressure-sensitive adhesive sheet is applied to an adherend comprising such resin materials, then the gas generated from the adherend will cause blisters (swelling) between the adherend and the pressure-sensitive adhesive sheet.
In order to solve such problems as described above, a pressure-sensitive adhesive sheet has been proposed which is formed therein with through-holes having a hole diameter of 0.1 to 300 μm with a hole density of 30 to 50,000 holes/100 cm2 (Patent Document 1). Such a pressure-sensitive adhesive sheet causes air and gases on the side of the pressure-sensitive adhesive face to escape via the through-holes towards the side of the surface of the pressure-sensitive adhesive sheet, thereby to allow for preventing air entrapments or blisters in the pressure-sensitive adhesive sheet.
In the pressure-sensitive adhesive sheet of Patent document 1, however, through-holes would possibly be visible by the naked eye depending on the hole diameter of the through-holes and/or the material of the base material, so that the appearance of the pressure-sensitive adhesive sheet might have not been necessarily good.
Accordingly, a pressure-sensitive adhesive sheet has been proposed in which a base material defined with its surface roughness (Ra), chroma (C*), lightness (L*) and contrast ratio is used, as well as defined with the hole diameter of through-holes in the base material and a pressure-sensitive adhesive layer, the hole diameter of the through-holes at the surface of the base material, the outer diameter of melted portions formed by laser around the through-holes at the surface of the base material, and the outer diameter of thermally deformed portions formed by laser around the through-holes or around the melted portions at the surface of the base material (Patent Document 2). The appearance of such a pressure-sensitive adhesive sheet is basically comparable to that of a pressure-sensitive adhesive sheet having no through-holes.
Patent Document 1: Domestic re-publication of PCT international application No. 2004/061032
Patent Document 2: Domestic re-publication of PCT international application No. 2005/121268